This invention relates to an improved attachment method and assembly for securing haptics to intraocular lenses. At the present time haptics, which are used to center and support intraocular lenses within the eye, are attached to the lenses by a variety of mechanical means. In one method peripheral material integral with the lens is carefully machined into supports of the desired shape and dimensions. This method is inherently expensive and is subject to breakage of the relatively brittle supports.
U.S. Pat. Nos. 4,615,701, 4,617,023, and 4,585,454 describe several intraocular lens designs wherein haptics are secured with currently available techniques. U.S. Pat. No. 3,996,626 discloses a variety of haptic designs and describes a method of securing haptics by means of a beading technique involving the melting of the end of a metal haptic and then securing the haptic to the lens by the forces generated by the displacement of lens material; it does not appear to take into account the differences in expansion coefficients between the lens material and the metal. U.S. Pat. No. 4,242,761 teaches the use of threaded bores into which haptic filaments can be expanded by force or heat; however, the method can cause foreign material to be trapped between the threads and the haptic only to be released later after implantation. U.S. Pat. No. 3,994,027 describes another method for anchoring metal haptics by heating the haptics ohmically and then pressing them into the lens body. This patent also appears to ignore the problems of bonding dissimilar materials and the differences in thermal expansion between the haptic and the lens.
Similarly, U.S. Pat. No. 4,104,339 describes a method whereby heated wires or haptics are pressed into the lens body by melting the lens material thereby wetting the heated wire to form a bond between the wire and the lens. The patent also describes the use of a heated point to melt the lens material to hold either a metal or plastic haptic which has been inserted into a chordal hole in the lens and depends only on the melting of the lens material for the fusing operation. U.S. Pat. No. 4,588,405 discloses a method in which a plastic haptic is inserted into a hole in the periphery of the lens and then enlarged at the inner end by melting the haptic by means of a heated rod inserted into a blind hole intersecting the chordal opening. While this method insures that the haptic will not pull out of the hole, it does little to prevent rotation of the haptic within the hole since the melted material neither appears to conform to the walls of the hole nor does it wet the enclosing walls. For reference, FIGS. 1A and 1B show a typical, complete intraocular lens structure with two haptics representative of the prior art. While only two haptics have been shown in the interest of clarity, it is recognized that other numbers and shapes of supports or haptics have also been used. Two illustrations of prior art methods for fastening haptics are shown in FIGS. 2A and 2B. In FIG. 2A, heated point 35 is brought to bear onto the planar side of thermoplastic lens 1 so that lens material 36 is melted, thereby fusing haptic 2 to the lens. In FIG. 2B heated point 35, inserted into hole 37, contacts the end of haptic 2 so as to enlarge the end of the haptic by melting, thereby preventing withdrawal of the haptic, but since the haptic material does not appear to fill cavity 37, the haptic may still rotate. Regardless of which of the above methods is used, each lens and haptic assembly is expected to withstand a pull force of at least 50 grams in the direction of the haptic, and, of course, the generation of asperities which might cause eye irritation must be carefully avoided.
In the majority of examples of prior art, haptics are inserted into holes oriented axially or chordally in the intraocular lens body and anchored by the application of heat or mechanical force in combination with perhaps ultrasonic energy to facilitate joining of the parts. However, in all of the foregoing examples known to the inventor, each suffers from one or more defects such as the need to polish the intraocular lens surface after the fastening operation, the possibility of entrapping foreign material which could cause eye irritation and the possibility of excessively distorting the lens mechanically or thermally. In addition, while many of the extant configurations may resist a pull test of 50 grams, or may resist relatively strong twisting forces, they are not known to have both capabilities simultaneously.
It is therefore an object of this invention to produce an improved attachment method and assembly for attaching haptics to intraocular lenses.
A further object of this invention is to produce an attachment method and assembly for anchoring haptics to intraocular lenses whereby pull test strengths well in excess of the required 50 grams is achieved simultaneously with a high torque resistance, thereby increasing the reliability of the lens assembly.
Another object of this invention is to produce an attachment method which minimizes the possibility of optical distortion by neither melting nor overly stressing the lens material.
It is a still further object of this invention to provide the foresaid objectives in a viable manufacturing mode capable of high production yields in order to minimize the cost of fabrication of intraocular lens implants.